Copolymerization of vinyl acetate and a fluoromonomer in an aqueous medium

ABSTRACT

A process of preparing a copolymer of vinyl monomer such as vinyl acetate, vinyl propionate and vinyl trifluoroacetate, and of fluorinated monomers such as tetrafluoroethylene and trifluoroethylene, said copolymer having an alternating or substantially alternating distribution of vinyl recurring monomeric units and fluorinated recurring monomeric units in the copolymer backbone which comprises copolymerizing said monomers in an aqueous reaction medium comprising water and a water miscible organic co-solvent in an amount less than the amount sufficient to form a distinct organic co-solvent phase.

RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 424,441, filed Dec. 20, 1989,now U.S. Pat. No.5,070,162 which, in turn, is a continuation-in-part of application123,480, filed Nov. 20, 1987.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a process for the preparation of copolymers ofvinyl acetate and a fluoromonomer. More particularly, this inventionrelates to a process for preparing copolymers of vinyl acetate and afluoromonomer having a substantially alternating distribution of therecurring monomeric units derived from vinyl acetate and thefluoromonomer along the polymer backbone.

2. Prior Art

Typical copolymers based on tetrafluoroethylene orchlorotrifluoroethylene are disclosed in U.S. Pat. Nos. 3,624,250;4,123,602; 3,642,742; 4,513,129; 3,445,434; 3,847,881 and 2,468,664.U.S. Pat. No. 4,434,273 discloses perfluorovinyl ethers and copolymersof such materials with tetrafluoroethylene. U.S. Pat. Nos. 4,471,076 and4,500,739 disclose fluorocarbon polymers containing carboxy groups. U.S.Pat. No. 4,513,129 discloses copolymers of ethylene, tetrafluoroethyleneor chlorotrifluoroethylene and fluorovinyl compounds of the formula H₂C═CFR_(f) where R_(f) is a fluoroalkyl group of C₂ -C₁₀.

U.S. Pat. No. 4,482,685 discloses that copolymers of ethylene andchlorotrifluoethylene have been polymerized in an aqueous emulsion usingfree radical initiation. The free radical initiators include a widevariety of peroxide and oxidation-reduction systems. The polymercomposition can be adjusted by either the ethylene pressure or thereaction temperature. The physical or mechanical properties of thecopolymers formed depend not only on the polymer composition but also onthe degree of alternation of the monomers.

It is known to emulsion polymerize a variety of fluoropolymers. U.S.Pat. Nos. 3,857,827 and 4,025,709 disclose the emulsion polymerizationof polyvinylidene fluoride. U.S. Pat. No. 4,225,482 discloses theemulsion.

Improved barrier resistance of ethylene vinyl alcohol copolymers isdisclosed in U.S. Pat. No. 4,427,825 and the Background of the Inventionthereof, as well as related U.S. Pat. No. 4,468,427.

The above review of the art shows a great variety of fluoropolymers andcopolymers. Modena, et al. Vinyl Acetate and Vinyl Alcohol Copolymerswith Tetrafluoroethylene, European Polymer Journal, 1967, Vol. 3, pp.5-12, Pergamon Press Limited, England (1967) discloses a specific classof copolymers of vinyl acetate and vinyl alcohols. Copolymers oftetrafluoroethylene and vinyl acetate are disclosed in Great BritainPatent 583.482. U.S. Pat. Nos. 3,006,881 and 3,043,823 disclose theemulsion polymerization of polychlorotrifluoroethylene.

SUMMARY OF THE INVENTION

This invention is directed to a process for forming a copolymercomprising 40 to 60 mole percent of fluorinated units having the formula(R₁ R₂ C--CR₃ F) wherein R₁, R₂ and R₃ are the same or different and areselected from H and F, and R₃ is Cl, when R₁ and R₂ are F; andcorrespondingly from 60 to 40 mole percent of vinyl units having theformula --(H₂ C--CHR_(x))--, wherein R_(x) is a radical of theformula-O₂ CR_(y) and wherein R_(y) is a

radical selected from the group consisting of --CH₃, --C₂ H₅, --CF₃ and--C₂ F₅, wherein the fluorinated units and vinyl units are in asubstantially alternating distribution as determined by 1H FourierTransform Nuclear Magnetic Resonance Spectroscopy; said processcomprising copolymerizing a vinyl monomer of the formula: H₂ C═CHO₂CR_(y) and a fluoromonomer of the formula R₁ R₂ C═CFR₃ in an aqueousreaction medium consisting essentially of water and one or more watermiscible organic co-solvents in the absence or in the substantialabsence of a distinct organic co-solvent phase in the reaction mixtureand in the presence of an initiator; and maintaining the molar ratio ofvinyl monomer to fluoromonomer dissolved in the reaction medium constantor substantially constant during said co-polymerizing to form acopolymer having an alternating or substantially alternatingdistribution of monomeric units derived from said vinyl monomer and saidfluoromonomer in said copolymeric backbone.

Maintaining the molar ratio at vinyl monomer to fluoro monomer in thereaction medium constant or substantially constant during thepolymerization.

The ester groups of the copolymer formed by the process of thisinvention can be hydrolyzed to form a crystalline copolymer whichincludes monomeric units derived from the vinyl monomer and thefluoromonomer in an alternating or substantially alternating fashionwith no or substantially no blocks in which either the fluorinated unitsor vinyl units predominate. This results in single melting point peakwhen measured using a DuPont 990 Thermal Analyzer Differential ScanningCalorimeter (DSC). The procedure is to heat a 7 to 10 mg sample at 20C/minute from room temperature to 300° C.; followed by a quick quench inliquid nitrogen and reheating to determine reproducibility. Thealternating or substantially alternating distribution of the fluorinatedmonomeric units and the vinyl monomeric units are important for theimproved barrier properties of the hydrolyzed copolymer.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is a method of copolymerization of a vinyl monomerof the formula H₂ C═CHO₂ CR_(y) where R_(y) is as described above and afluoromonomer of the formula R₁ R₂ C═CFR₃ where R₁, R₂ and R₃ are asdescribed above. The product is a copolymer in which the fluorinatedmonomeric units and the vinyl monomeric units are distributed in thepolymeric backbone in an alternating or substantially alternatingfashion with no or substantially no blocks in which either thefluorinated units or vinyl units predominate.

One critical requirement is that the copolymerization must be conductedin an aqueous medium which comprises a solution of water and a watermiscible, inert organic co-solvent, which medium contains no orsubstantially no distinct organic co-solvent phase. The reaction mediumis critical to obtaining the desired copolymer. The aqueous mediumserves several useful functions. For example, the medium is a solventfor the required amounts of vinyl monomer and fluoro monomer. The vinylmonomer is soluble in the aqueous medium and is typically soluble inboth water and the co-solvent. However, the fluoro monomer is generallynot soluble in water, but use of the co-solvent increases the solubilityof the fluoromonomer in the aqueous reaction medium. The solubility ofthe reactive monomers allows for the reaction of the monomer in thedesired sequence and molar ratios to provide for a more uniformdistribution of fluoromonomer and vinyl monomer along the polymer chain.

Another function served by the co-solvent in the aqueous reaction mediumis that it swells the copolymer particles. This results in pores whichallow the reaction medium containing the dissolved monomers in thedesired proportions to penetrate the particles so that the reactivemonomers can have access to the growing polymer chain in the requiredproportions to form a copolymer having the desired distribution ofrecurring monomeric units. In the absence of such swelling, theparticles would grow fluorinated blocks and vinyl blocks would form inthe liquid phase. The result would be branched copolymers rather thanlinear copolymers and to block copolymers rather than alternatingcopolymers. The organic co-solvent while swelling polymer particlesshould not be preferentially absorbed by the polymer particles.Otherwise, the concentration of the organic solvent in water willdecrease with growing accumulation of the polymer, which would upset thecopolymerization equilibria and gradually lead to block copolymerformation. The solvent should be substantially unreactive with vinylacetate and the fluoromonomer radicals. By substantially unreactive itis meant that the reactive growing copolymer chains do not react withthe solvent to remove a hydrogen atom from the solvent resulting inpremature polymer chain termination chain transfer reactions.

Organic solvents which can function as described herein above can beused in the practice of this invention. The water used is preferablydeionized or distilled water. Preferred solvents include but are notlimited to acetic acid, t-butanol, acetonitrile, and methyl acetate withacetic acid or mixture thereof being most preferred.

The aqueous medium includes an amount of the co-solvent which issufficient to function as described above. In general, the amount ofco-solvent is from about 1% by weight to about 99% by weight based onthe total weight of the aqueous medium. The amount of co-solvent ispreferably from about 10% by weight to about 75% by weight based on thetotal weight of the medium and is more preferably from about 20% byweight to about 60% by weight on the aforementioned basis. The amount ofthe aqueous medium employed in the process is sufficient to maintain auniform and homogeneous solution of the reactant comonomers andinitiator at the initiation of the reaction. It is preferred to use fromabout 10 to about 75, more preferably from about 10 to about 50, andmost preferably from about 10 to about 30 parts by weight of aqueousmedium per part by weight of the comonomers consumed.

The fluoromonomer for use in the practice of this invention are those ofthe formula R₁ R₂ C═CFR₃ where R₁, R₂ and R₃ are as described above. Anysuch fluoromonomers can be employed in the practice of this invention.Preferred fluoromonomers are tetrafluoroethylene and trifluoroethylene.Most preferred fluoromonomer is tetrafluoroethylene.

Vinyl monomers for use in the practice of this invention are those ofthe formula: H₂ C═CHO₂ CR_(y) wherein R_(y) is as described above.Preferred vinyl monomers are vinyl acetate, vinyl trifluoroacetate andvinyl propionate. The vinyl monomer for use in the most preferredembodiments of this invention is vinyl acetate.

The relative amounts of fluoromonomer and vinyl monomer employed willdepend on the desired molar ratio of recurring units derived from thesemonomers in the copolymer. In general, the amount of fluoromonomeremployed is from about 40 to about 60 mole percent based on the totalmoles of copolymerizable species in the reaction mixture, and the amountof vinyl monomer employed is from about 40 to about 60 mole percent onthe aforementioned basis. In the preferred embodiments of the invention,the amount of fluoromonomer employed is from about 45 to about 55 molepercent and the amount of vinyl monomer employed is from about 45 toabout 55 mole percent, and in the most preferred embodiments, the amountof fluoromonomer employed is from about 48 to about 52 mole percent andthe amount of vinyl monomer employed is from about 48 to about 52 molepercent. In the embodiment of choice, the amount of fluoromonomeremployed is about 50 mole percent and the amount of vinyl monomer isabout 50 mole percent based on the total moles of copolymerizablespecies.

In addition to the required fluoromonomer and vinyl monomer thecopolymers of the present invention may include other copolymerizablemonomers such as olefins as for example, ethylene, propylene, and thelike. In the preferred embodiments of the invention, from 0 to about 10mole percent (based on the total moles of copolymerizable species) ofother copolymerizable monomers may be employed, and in the morepreferred embodiments, from 0 to about 5 mole percent of such monomer isemployed. In the most preferred embodiments of the invention, no orsubstantially no other copolymerizable monomer is used.

The reaction is carried out in the presence of a copolymerizationinitiator. The type of initiator employed may vary widely. The onlyrequirement is the ability to initiate the reaction. The initiator ispreferably a free radical initiator which can include peroxy-typecatalysts, and oxidation-reduction systems. Oxidation-reduction systemsare preferred. Useful oxidation-reduction systems are described in U.S.Pat. No. 4,469,854 hereby incorporated by reference.

An initiator useful in the process of the present invention is a redoxcatalyst system employed in an aqueous media. The redox system comprisesan oxidizing agent and a reducing agent. These include water solubleinorganic peroxides such as perchlorates, perborates, persulfates,perphosphates, percarbonates, barium peroxide, zinc peroxide, andhydrogen peroxide. Particular examples include sodium, potassium,calcium, barium, and ammonium salts of persulfuric acid andperphosphoric acids. The preferred oxidizing agents include thefollowing water soluble peroxide compounds: alkali metal and alkalineearth metal water soluble salts of persulfuric acids such as the saltsof sodium, potassium, barium, and the ammonia salts of persulfuric acid.The preferred salts are ammonia salts of persulfuric acid. The preferredsalts are ammonium persulfate ((NH₄)S₂ O₈) and potassium persulfate (K₂S₂ O₈).

The amount of oxidizing agent employed is generally from about 0.0001 to1.0, preferably from about 0.001 to about 0.8, and more preferably fromabout 0.01 to about 0.5 parts by weight based on 100 parts of the totalcomonomers.

The reducing agents include ascorbic acid, and ammonium and alkali metalsulfur-containing salts such as the sulfites, thiosulfates, bisulfites,hydrosulfites of ammonia, sodium, potassium, rubidium, and cesium. Ofthese, ascorbic acid is preferred. The amount of reducing agent employedis generally from about 0.001 to about 1.0, preferably from about 0.00to about 0.8, and more preferably from about 0.01 to about 0.5 parts byweight based on 100 parts of the total comonomers.

The reaction conditions can be varied depending on the extent ofpolymerization and the final product composition which is desired. Ingeneral, the temperatures range from between about -20° C. to about 70°C., preferably from about 0° C. to about 65° C., more preferably fromabout 5° C. to about 55° C. and most preferably from about 10° C. toabout 45° C.

The pressure is maintained by introducing tetrafluoroethylene and aninert gas such as nitrogen. The preferred pressure under which thereaction is conducted is from about 20 to about 300 pounds per squareinch guage (psig), preferably from about 100 to about 275 psig, and morepreferably from about 150 to 250 psig.

The time of polymerization depends upon the amount of copolymer to bepolymerized. The polymerization continues until the desired amount ofcopolymer is formed. Typically, polymerization times of from about 10minutes to about 12 hours may be employed. A preferred polymerizationtime is between about 0.25 and 5 hours, more preferably between 0.5 and2 hours.

To achieve a substantially alternating distribution or an alternatingdistributing of fluorinated units and vinyl units, the initial andcontinuous ratio of the monomer feed is important. The relative feedratio can be determined by experimentation as set forth in theaccompanying Examples and Comparative Examples. The feed amounts dependupon the specific monomers used and the conditions of copolymerizationdesired.

A preferred method of the present invention is the copolymerization oftetrafluoroethylene and vinyl acetate. The tetrafluoroethylene isprovided as a gas under pressure. Part of the vinyl acetate is initiallyprovided in solution in the aqueous medium. Preferably the pressure ofthe tetrafluoroethylene is maintained at a desired level during thereaction. This level is preferably a constant pressure in the range offrom about 10 to about 300 psi. The consumption of tetrafluoroethyleneis measured and concurrently the amount of vinyl acetate which wouldreact with the consumed tetrafluoroethylene is added. The vinyl acetateis added to the aqueous medium in an amount so that it will all bedissolved. A preferred rate of addition of vinyl acetate is an initialamount in the range of up to about 10 gm of vinyl acetate per liter ofaqueous medium with preferably from about 1 to about 7 grams and morepreferably from about 2.5 to about 5 grams of vinyl acetate. Vinylacetate is then added as used. This can be measured based on the amountof tetrafluoroethylene consumed. The copolymer produced is in the formof swollen particles.

The preferred copolymerization process of the present invention proceedsin a sealed reactor in several basic steps. Water and co-solvent areadded to the reactor. The reducing agent (i.e., ascorbic acid) is addedwith the water. An aqueous solution of the fluoro-surfactant and bufferare optionally added to the reactor. Vinyl monomer is added to thereactor in an initial amount which does not exceed its solubility in theaqueous medium. At this time, it is preferred to purge with nitrogen orother inert gas. Optional additives such as molecular weight regulators,anticoagulants, buffer, and antifoaming agents can be added in the firststep. The fluoromonomer is then added. The oxidizing (i.e., ammoniumpersulfate) agent is then added, preferably in a water solution. Thereactor is preferably maintained at the desired operating pressure bythe continuous addition of fluoromonomer. Vinyl monomer is added duringthe reaction. It should not be added in amounts which exceed itssolubility in the aqueous medium. Preferably, the rate of addition isbased on the rate of fluoromonomer consumption. In the final step, thereaction is stopped by venting unreacted monomer from the reactor andthe copolymer is collected.

In a preferred embodiment of the process, the charge to the reactorinitially contains deionized water, co-solvent, the vinyl monomer, chaintransfer agent, and the reducing agent. The reactor is sealed andpreferably purged and pressurized with an inert gas such as nitrogen.After this, the fluoromonomer, preferably tetrafluoroethylene, ischarged to the reactor. A solution of the oxidizing agent in water isthen pumped into the reactor. As the reaction proceeds, additionalamounts of the water solution of the oxidizing agent can be added. Thefluoromonomer pressure is maintained constant throughout the reactionand vinyl monomer continuously added. The conditions under which thereaction proceeds are discussed above.

The copolymers produced according to the process of the presentinvention are thermoplastic polymers containing from about 40 to about60 mole percent, preferably from about 45 to about 55 mole percent andmore preferably from about 48 to about 52 mole percent vinyl units andcorresponding amounts of fluorinated units along the copolymer chain.The copolymer produced has a uniform distribution or a substantiallyuniform distribution of vinyl monomer and fluoromonomer along thepolymer molecule chain. In a copolymer having about 50 mole percent ofrecurring units derived from fluoromonomer and about 50 mole percent ofrecurring units derived from vinyl monomer the recurring units arealternating or substantially alternating. The procedure for determiningdegree of alternation is by ¹ H Fourier Transform Nuclear MagneticResonance Spectroscopy. For the purpose of the present inventionsubstantially alternating is at least about 30 mole percent alternatingas measured by this procedure. Preferably alternating values are fromabout 50 to about 90 mole percent, more preferably from about 60 molepercent to about 80 mole percent, and most preferably from about 70 molepercent to about 80 mole percent. It is believed that there are amountsof end groups, and short segments such as dimers and maybe some trimerswhich are not considered blocks and which do not significantly alter theproperties of a copolymer of the present invention.

The copolymer having units derived from the vinyl ester monomer can behydrolyzed to form vinyl alcohol by suitable means. A preferred methodis by contacting the ester copolymer, in a solvent, with a strong basesuch as sodium hydroxide. A useful solvent is an alcohol such asmethanol. The typical hydrolysis can be conducted at from about -10° C.to about 100° C., depending on the boiling point of the solvent.Depending on temperature, the reaction can be conducted at from about 30minutes to about 24 hours. It is convenient to hydrolyze at atmosphericpressure.

The hydrolyzed copolymer wherein the vinyl unit is hydrolyzed to form avinyl alcohol and where R₃ is H or F has a crystalline nature due to thestructural relationship of the two major units. In particular, thepolymer has a single peak when measured using a Differential ScanningCalorimeter (DSC). The DSC used in the present invention is a DuPont9900 thermal analyzer using a 7 to 10 mg sample heated at a rate of 20C. per minute from room temperature 300 C. The samples are quicklyquenched in liquid nitrogen and reheated to determine reproducibility.

The hydrolyzed copolymer made by the method of the present invention hasno detectable amounts of either of a fluoromonomer derived rich or avinyl monomer derived rich phases to result in separate peaks whenmeasuring the DSC of the copolymer according to the process recitedabove; or which are apparent when a sample of the composition is viewedunder a Transmission Electron Microscope (TEM) at a magnification of15,000 to 25,000 times.

The molecular weight of the hydrolyzed copolymer of the presentinvention can be varied as desired. The intrinsic viscosity of thecopolymers made by the method of the present invention measured at 35°C. in dimethylformamide (DMF) according to the ASTM D-1238 procedure isfrom about 0.1 to about 2.5, preferably from about 0.2 to about 1.5,more preferably from about 0.3 to about 1.0 and most preferably fromabout 0.5 to about 0.9.

The hydrolyzed copolymer made by the method of the present invention isuseful for making a variety of articles. In particular, it has beenfound to have exceptional resistance to permeation by gases such asoxygen. It is useful to make articles having one or more layers of thispolymer where oxygen permeation or improved oxygen barrier is criticalsuch as in films and bottles. It also has improved resistance to watervapor transmission. This is believed to be a result of the tightlypacked crystalline structure of the hydrolyzed copolymer and that thefluorinated and vinyl units are substantially alternating indistribution along the copolymer chain.

Films can be made by conventional film forming processes includingcasting and extruding. The film can be used alone or in combination withother layers as a laminate formed by coextrusion or by building upseparate layers of film. The use of adhesive layers is optional anddepends on the composition of the adjacent film layers.

A particularly convenient method of production of film laminates is thesimultaneous coextrusion methods are well known in the art.

The film and film laminates made by the present invention may beoriented by conventional means and/or embossed as desired.

In addition to making films, and film laminates, the copolymer can beformed by other forming processes including blow molding to form bottlesas well as molded parts and formable sheets. The copolymer can becompounded with conventional additives known in the art. Such additivesinclude fillers. Other polymeric materials such as impact modifiers, andinhibitors of oxidative, thermal, and ultraviolet light degradation,lubricants and mold release agents, colorants including dyes andpigments, fibers and particulate filler and reinforcements,plasticizers, etc.

Compositions containing the copolymer can be prepared by melt blendingin a closed system such as an extruder or other conventionalplasticating devices. Alternately, the polymer can be processed byprecipitation from solution, blending or by dry mixing with othercomponents followed by melt fabrication of the dry mixture by extrusionor molding. In addition to the articles mentioned above, the copolymercan be used in a variety of articles made by conventional fabricationmethods to form tubing sheet, fibers and oriented fibers, and wirecoating.

Several examples are set forth below to illustrate the nature of theinvention and the manner of carrying it out. However, the inventionshould not be considered as being limited to the details thereof. Allparts are by weight unless otherwise indicated.

COMPARATIVE EXAMPLES 1-3 EXAMPLES 1-4

The following examples illustrate the preparation of a copolymer oftetrafluoroethylene (TFE) and vinyl acetate (VAc) in accordance with themethod of the present invention. Each of the following copolymers wasmade in a 0.5 or 4 liter reactor as indicated by volume requirement. Thevinyl acetate monomer was provided as a liquid and the TFE fed as a gas.The atmosphere was a mixture of TFE and nitrogen. Initially, the reactorwas charged with water, vinyl acetate, acetic acid (AcOH) and ascorbicacid as indicated. Nitrogen (N₂) was added. The stirrer was operated at1500 rpm. TFE was added to the indicated pressure and the reactor closedand heated. An ammonium persulfate (APS) solution in water was injectedto initiate polymerization. In Comparative 1, after the initial charge,VAc was added at 25 g/hour. In Comparative 3, after the initial charge,no additional VAc was added. In Example 1 after the initial charge,additional VAc was added at the following rates: 0-4 minutes, 0 VAc;4-12, minutes, 40 g/hour; 12-16 minutes, 149 g/hour 16-24 minutes, 213g/hour; 24-28 minutes, 128 g/hour; and 28-34 minutes 170 g/hour. InExample 2, after the initial charge, additional VAc was added at thefollowing rates: 0-15.5 minutes, 0 VAc; 15.5-25.5 minutes, 20 g/hour;25.5-35.5 minutes, 15 g/hour; 35.5-45.5 minutes, 10 g/hour; 45.5-95.5minutes, 17 g/hour; 95.5-135.5 minutes, 21 g/hour. The polymerizationwas allowed to be conducted at the indicated temperatures for theindicated time. A white granular solid was formed and collected on acoarse frit. The polymer was washed with water and dried at theindicated conditions. The copolymers were analyzed by elemental analysisfor the percents by weight of C, H and F. The intrinsic viscosity [n]was measured at 35° C. in dimethyl formamide (DMF).

The reaction parameters and test results are summarized below in Table1.

                  TABLE 1                                                         ______________________________________                                                     Comp 1   Comp 2   Comp 3  Ex 1                                   ______________________________________                                        VAc, g (initial)                                                                           23       15       15       5                                     VAc, g/hr addd                                                                             25       15       --      *                                      TFE, psi     150      150      150     150                                    N.sub.2,psi 75                                                                             75       75       75       75                                    H.sub.2 O ml 800                                                                           800      150      150     800                                    AcOH, ml     200      200      --      200                                    APS, mg/ml H.sub.2 O                                                                       300/10   300/10   0.1     300/10                                 STIR RATE, rpm                                                                             1500     1500     1500    1500                                   Tx, t min    40       39       60       34                                    Rx, T. °C.                                                                          58-62    6-61     65-76   25-30                                  Dry T (°C.)/P (mm)                                                                           65/--    65/1    50/1--                                 Yield, g     52.2     37.9     25.1    149.1                                  FAc:TFE (mode                                                                              1.1:1    1.1:3    1:1.2   1:1.05                                 ratio)                                                                        C, wt. %     40.53    36.72    36.18   38.37                                  H, wt. %      3.43     2.61     2.60    2.86                                  F, wt. %     40.08    46.51    39.80   41.16                                  [n]           0.85    0.6      --       0.32                                  Hydrolysis   Comp 4   Comp 5   Comp 6  Ex. 5                                  DSC          double   double   could not                                                                             single                                              peak     peak     be      peak                                                                  hydrolyze                                      ______________________________________                                                      Ex. 2     Ex. 3     Ex. 4                                       ______________________________________                                        VAc, g (initial)                                                                             5        2.5 g/--  4.6                                         VAc, g/hr added                                                                             *          60        50                                         TFE, psi      150       150       150                                         N.sub.2 , psi  75        75        75                                         H.sub.2 O ml  800       800       1600                                        AcOH, ml      200       200       400                                         APS, m/ml H.sub.2 O                                                                         150/10    300 mg/10 600 mg/10                                   STIR RATE, rpm                                                                              1500      1500      1500                                        Rx, t min     135.5     130       130                                         Rx T, °C.                                                                            59-60     60-62     59-61                                       Dry T (°C)/P (mm)                                                                    --        85/--     65/--                                       Yield, g      82.2      19.1      32.5                                        VAc:TFE (mode ratio)                                                                        1.1:1     1.2:1     1.3:1                                       C, wt. %      37.83     40.21     36.82                                       H, Wt. %       2.90      3.47      2.62                                       F, wt. %      44.17     38.07     42.79                                       [n]            0.77      0.92     --                                          Hydrolysis    Ex. 6, 7  Ex. 8     Ex. 9                                       DSC           single    single    single                                                    peak      peak      peak                                        ______________________________________                                         *See above                                                               

COMPARATIVE 4

Comparative 4 illustrates the hydrolysis of a tetrafluoroethylene, vinylacetate copolymer made from Comparative 1. 46.5 grams of the copolymerwere dissolved in 465 ml of methanol with 21 ml of a 50 percent aqueoussodium hydroxide solution under a nitrogen atmosphere. The reactantswere heated for 1 hour under reflux. The solution was cooled andfiltered through a 5 micrometer filter. 47 ml of concentrated HCl wasadded to achieve a pH of 1. The solution was precipitated and washedwith water. The resulting polymer was dried overnight at 85° C. in acirculating air oven. 31.24 g of a light yellow polymer was recovered.The thermal gravimetric analysis (TGA) gave a 5 percent weight loss by370° C. with a major weight loss at greater than 400° C. Thedifferential scanning calorimetry (DSC) testing indicates a main meltingendotherm at 204° C. on cooling from 300° C. The intrinsic viscosity was0.63 measured in DMF at 35° C.

The double peak observed upon DSC testing is believed to indicate anexcess of vinyl acetate initially and during the copolymerization. Eventhough the VAc: TFE mole ratio was 1.1:1 in the copolymer, it isbelieved that there is an imbalance of monomers due to lack ofco-solvent causing large blocks of TFE rich segments and/or VAc richsegments.

EXAMPLE 5

Following is the procedure for the hydrolysis of a vinylacetate/tetrafluoroethylene (VAc/TFE) copolymer of Example 1 to vinylalcohol/ tetrafluoroethylene (VOH/TFE) copolymer. 25 grams of theVAc/TFE made in Example 1 were fed to a 3 neck 100 ml round bottom flaskcontaining a stir bar and a thermometer as well as a water condenser anda nitrogen inlet. The flask contained 250 ml of methanol, 10.5 ml of 50percent aqueous sodium hydroxide plus 18.5 ml of water. The mixture washeated an d refluxed at 67° C. for 2 hours. A hazy solution formed withsome undissolved material apparent. The polymer solution wasprecipitated in two portions, with each portion into 600 ml of water ina Waring Blender. The mixture was filtered and acidified withconcentrated HCl to a pH of 5. The solids were collected and were washedthree times in 600 ml of water and then dried in a circulating air ovenat 85° C. overnight. 13.0 grams of cream colored solids were obtained(66.7% yield). The TGA showed the samples to be stable up to 350° C. Thesamples began degrading above 350° C. There was an 18.5% residue at 850°C. DSC was measured upon heating to 300° C., quenching and reheating.The following melting point was observed Tm=206° C. Upon reheating, theTm was measured at 203° C. There was only one melting point. Thecopolymer was formed into a film by compression at 230° C. using anApollo platen press. The film made was about 3 inches in diameter and 3mils thick. The film was examined by TEM (Transmission ElectronMicroscope) and observed to be uniformly spherulitic. The spheruliteswere about 0.3 um in diameter with a lamellae 20 um in width. Thismaterial was found to have 34.87 wt. % C, 2.03 wt. % H, and 49.36 wt. %F. The ratio mole of VOH:TFE was 1.20:1. The sample was pressed into afilm tested for oxygen permeability using an O-Tran 1000 oxygenpermeability tester made by Mocon Corp. At 0 percent relative humidity,a 3 mil thick film had 0.013 cc/mil/100 in/day. The sample was testedat. 100 percent relative humidity and had 0.08/cc/mil/100 sq in/per day.

EXAMPLE 6

Example 6 is an example of hydrolyzing 25 g of the vinyl acetate/TFEcopolymer made in Example 2. The vinyl acetate/TFE copolymer washydrolyzed in a 500 ml flask with 10 ml of a 50 percent aqueous sodiumhydroxide (NaOH) solution in 250 ml methanol (MeOH) and 5 ml water,under N₂ in presence of heat. The procedure was similar to that ofExample 6 except it was refluxed for 1 hour. The result was a fairlyclear amber very viscous solution. About 16 g of Celite filter aid wasadded and it was filtered. The filtrate was acidified with a total of 10ml of concentrated hydrochloric acid. The polymer was precipitated inwater in a Waring Blender. After filtering, the solids were collectedand dried at about 85° C. overnight. About 17.2 g of an off whitepolymer was recovered. The viscosity at 35° C. in DMF was measured andindicated a single melting point at about 213° C. Upon reheating, afterquenching from 300° C., the melt point appears at 211° C.

EXAMPLE 7

Example 6 was repeated to make additional VOH/TFE copolymer. Thecopolymer has an intrinsic viscosity 35° C., DMF of 0.62 and a moleratio of VOH/TFE of 1:1.2. The copolymer was molded into film and quickquenched. The film was heated at various temperatures in anenvironmental chamber for 15 minutes and drawn. The draw ratio, andelongation to break of the films annealed at different temperatures issummarized in Table 2. Crystallininty of the film was measure by X-ray.The initial unoriented polymer was 30% crystalline.

                  TABLE 2                                                         ______________________________________                                        Temp          Draw    % Crystallinity                                         ______________________________________                                         90° C.                                                                                3:1   --                                                      100° C.                                                                               4.2:1  33%                                                     110° C.                                                                                3:1   --                                                      120° C.                                                                              1.87:1  --                                                      140° C.                                                                              Break   45%                                                     ______________________________________                                    

The maximum elongation was at 100° C. with little increase incrystallinity. As the temperature increased crystallinity increased withthe film breaking at 140° C. The polymer was tough and reasonably clear.This indicated small crystallites and probable use for packagingapplication.

EXAMPLES 8, 9

The copolymer of Examples 3, 4 and Comparative 2 were hydrolyzed asExamples 8, 9 and Comparative 5 respectively according to the procedureof Ex. 7. The details and results ar summarized in table 3 below:

                  TABLE 3                                                         ______________________________________                                                     Comp 5    Ex 8    Ex 9                                           ______________________________________                                        Copolymer Ex   Comp 2      Ex 3    Ex 4                                       VAc/TFE (g)    30.8         25     25.4                                       MeOH (ml)      30.8        250     254                                        NaOH (ml)       11.41      11.8     9.4                                       H.sub.2 O (ml) 6            6       4                                         Reflux @67° C. (hr)                                                                   1            1       1                                         HCl (ml)       5            12      10                                        VOH/TFEg       14.9        17.6    17.3                                       TGA (Degrad T °C.)                                                                    400 C.      400 C.  350 C.                                     DSC initial heating                                                                          202/22      204     226                                        cool from 300° C.                                                                     198/222     204     225                                        [n]             0.55        0.65    0.49                                      ______________________________________                                    

COMPARATIVE 6

Hydrolysis of the copolymer made in Comparative 3 was attemptedgenerally following the procedure used in Example 5, using 10 grams ofthe copolymer of Comp. 3, 150 ml of methanol, 3.4 ml of 50 percentaqueous sodium hydroxide.

The polymer was observed to swell and float to the top of the methanol.The product was insoluble. After one and a half hours of reflux at 67°C., 0.9 ml of NaOH was added, after 3 hours 25 ml of NaOH with nochange. The mass was left for a weekend at room temperature but stilldid not dissolve. The result was a reddish gelatinous mass.

It is believed that the absence of co-solvent does not allow the uniformdiffusion of comonomers into the growing copolymerizing particles. Thisresults in the formation of TFE rich and VAc rich segments. The presenceof the TFE rich segments prevents solubilization of the copolymer duringhydrolysis resulting in the gelatinous mass.

The presence of co-solvents will cause swelling of the growing polymerparticles and the uniform diffusion of comonomers into the particle.This results in the desired alternating copolymerization.

COMPARATIVE 7

To a four liter stainless by a Zipperclav reactor system was added 600ml of water treated by a Millipore system and degassed for one hour bysparging with nitrogen. Add 0.8 gram ammonium persulfate in 20 ml water(degassed), 130 ml freshly distilled vinylacetate (degassed) and thesystem is pressurized with 45 psi N₂ and 90 psi TFE. While stirring at500 RPM, the reactor is heated to 75° C. and this temperature ismaintained for 6 hours. The pressure dropped from 160 psi to 110 psi.The reaction mixture was then cooled and 137 grams of copolymer wasrecovered. Elemental analysis was C (44.42%), H (4.36% and F (28.34%)which indicates a comonomer ratio of 2: VAC:TFE. It was not possible toobtain a meaningful intrinsic viscosity since 58% of it was insoluble inDMF. No NMR studies could be made again because no solvents could befound. Analysis by DSC reveals a melting point at about 325° C., whichindicates the presence of polytetrafluoroethylene.

Twenty five grams of the copolymer, 250 ml methanol, 5 ml water and 9.4ml of 51.2% aqueous caustic was refluxed for 2.5 hours. The copolymerdid not dissolve but formed a spongy mass. The total reaction mixturewas cooled to room temperature and then poured into water in a Waringblender. The polymer was washed with additional water and then dried ina circulating air oven at 100 C. overnight. Recovered 16.2 g (75%). Thelow yield would indicate that the vinylalcohol rich polymers (largeblocks of homopolymers) are soluble in the precipitating media. It wasnot possible to obtain an intrinsic viscosity since 75% of the polymerwas insoluble. Infra red analysis indicated that 40% of the acetategroups were not hydrolyzed. Elemental analysis of C (38.24%), H (4.2%)and F(33.36%) suggests partial hydrolysis. TGA indicates a continuingweight loss with 5.6% being lost at 300 C. DSC shows an initial T_(m) at210° C. and after cooling from 300 C., a reheat of T_(m) of 196° C. Thelowering of the melting point again indicated poor melt stability.Heating a sample in the DSC to 350° C. again reveals a melting point atabout 325° C. indicating PTFE. The copolymer could not be molded at 250°C. due to incomplete melting and decomposition.

In an attempt to obtain a copolymer ratio closer to 1:1, thepolymerization was repeated using 60 psi N₂ and 120 psi TFE. 253 gpolymer was recovered which was 80% insoluble in DMF. Several elementalanalyses indicated a comonomer ratio of from 1:1.2 to 1:1.7 VA:TFE, anon-homo- geneous product. DSC indicates a much larger melting peak at325° C.; a greater amount of PTFE being produced. Attempted hydrolysisagain was complicated by insolubility and only 50% of the acetate groupswere hydrolyzed. TGA indicates decomposition starting at about 250° C.The DSC had an initial T_(m) 211° C. and after cooling from 300° C. areheat T_(m) at 204° C. Heating to 350° C. revealed a large T_(m) at325° C. This copolymer could not be molded.

EXAMPLE 10

To a four liter zipperclav reactor is added 900 ml acetic acid, 900 mldeionized water, 0.31 g ascorbic acid, 16 ml vinyl acetate, and 5 mlisopropanol. The solution is sparged with nitrogen to remove oxygen andthe reactor sealed. The reactor is pressurized with 75 psi nitrogen and152 psi tetrafluoroethylene. The reaction mixture is stirred at 750 rpmand the temperature is 21° C. A solution of 0.2 g ammonium persulfate in25 ml is pumped into the reactor to initiate the polymerization. Withintwo minutes, polymerization begins as indicated by a drop in reactorpressure of about two pounds and an increase in reactor temperature toabout 24° C. Immediately, tetrafluoroethylene is fed to the reactor tomaintain a total reactor pressure of about 225 psi and vinylacetate (54ml) is pumped into the reactor concurrently to maintain stoichiometry.The total reaction time is about thirty minutes and the finaltemperature is 29° C. During the first 20 minutes, an additional 7 ml ofthe ammonium persulfate solution is added. At the end of the reaction,there is no tetrafluoroethylene being absorbed. The vinylacetate feed isstopped and the reactor vented. The copolymer is recovered, washed in aWaring blender with deionized water and then dried overnight at 100° C.in a circulating air oven. One hundred thirty three and five tenthsgrams of copolymer is recovered with an intrinsic viscosity of 0.74(DMF, 35° C.).

The copolymer is hydrolyzed by adding 50 g to 500 ml methanol, 10 mldeionized water and 13.7 ml of 51.2% aqueous NaOH and refluxing for 2.25hours. After cooling to room temperature, tramp dirt is removed byfiltration through #41 Whatman filter paper and the polymer is recoveredby adding the filtrate to 1500 ml of deionized water in a Waringblender. The precipitated copolymer is washed in the blender three timeswith 1500 ml portions of deionized water and then dried overnight at100° C. in a circulating air oven. Thirty Six and six tenths grams(94.5%) of the copolymer is recovered which has an intrinsic viscosityof 0.89 (DMF, 35° C.). Elemental analysis of carbon (33.15%), hydrogen(2.67%), and fluorine (53.07%) indicates a comonomer ratio of about 1:1.The initial melting point by DSC is 213° C. and after cooling from 300°C., the reheat melting point is again 213° C.

EXAMPLE 11

To a four liter Zipperclav reactor is added 1260 ml of acetic acid, 540ml of deionized water, 0.31 g of ascorbic acid, and 20 ml. of vinylacetate. The solution sparged with nitrogen to remove oxygen and thereactor is sealed and pressurized with 75 psi nitrogen and 150 psitetrafluoroethylene. The reactor temperature is 24° C. and is stirred at750 rpm. A solution of 0.26 g ammonium persulfate and 30 ml deionizedwater is degassed and 3 ml is pumped into the reactor to initiatepolymerization. Within four minutes, copolymerization begins asevidenced by a pressure drop and a temperature rise to 25° C.Immediately, tetrafluoroethylene is fed to the reactor to maintain aconstant pressure of about 225 psi and during the thirty minute reactionperiod, 46 ml of degassed vinylacetate is concurrently pumped into thereactor to maintain stoichometry. During the first twenty minutes of thecopolymerization, an additional 9 ml of ammonium persulfate solution ispumped into the reactor. The temperature rose to 28° C. during thepolymerization. At the end of the polymerization, no moretetrafluoroethylene is being absorbed so the vinylacetate feed isstopped and the reactor is vented. The copolymer is recovered and washedin a Waring blender with deionized water. After drying overnight at 100°C. in a circulating air oven, 105.6 g of copolymer is obtained with anintrinsic viscosity of 1.26 (DMF, 35° C.). The elemental analysisindicates a comonomer ratio of 1.05:1 VAC:TFE.

The copolymer is hydrolyzed by adding 50 g to 500 ml methanol, 10 mlwater and 13.4 ml of 51.2% aqueous HaOH and refluxing for three hours.After cooling to room temperature, 16 g of Celite filter aid is addedand the solution is filtered through #41 Whatman filter paper. Thecopolymer is precipitated into 1500 ml deionized water in a Waringblends and then washed an additional three times in the blender with1500 ml portions of deionized water. After drying overnight at 100° C.in a circulating air oven, 34.5 g (84%) of polymer is recovered havingan intrinsic viscosity of 1.69 (DMF, 35° C.). Elemental analysis ofcarbon (34.03%), hydrogen (3.06%), and fluorine (51.60%) indicates acomonomer ratio of 1.12:1 VAC:TFE. The initial melting point by DSC is213° C. and after tooling from 300° C., the reheat melting point is 211°C. It is believed that the lower yield of polymer is due to retention ofpolymer on the Celite filter cake.

While exemplary embodiments of this invention have been described, thetrue scope of the invention is to be determined from the followingclaims:

What is claimed is:
 1. A process of forming a copolymer comprising 40 to60 mole percent of fluorinated units having the formula (R₁ R₂ C--CR₃ F)wherein R₁, R₂ and R₃ are the same or different and are selected from Hand F, and R₃ is C1, when R₁ and R₂ are F; and correspondingly from 60to 40 mole percent of vinyl units having the formula (H₂ C--CHR_(x)),wherein R_(x) is a radical of the formula O₂ CR_(y) and wherein R_(y) isa radical selected from the group consisting of --CH₃, --C₂ H₅, --CF₃and C₂ F₅ wherein the fluorinated units and vinyl units are in asubstantially alternating distribution as determined by 1H FourierTransform Nuclear Magnetic Resonance Spectroscopy; said processcomprising copolymerizing a vinyl monomer of the formula: H₂ C═CHO₂CR_(y) and a fluoromonomer of the formula R₁ R₂ C═ CFR₃ in an aqueousreaction medium consisting essentially of a solution of water and one ormore water miscible co-solvent in the absence or in the substantialabsence of a distinct organic co-solvent phase in the reaction mixtureand in the presence of an initiator; and maintaining the molar ratio ofvinyl monomer to fluoromonomer dissolved in the reaction medium constantor substantially constant during said co-polymerizing to form acopolymer having an alternating or substantially alternatingdistribution of monomeric units derived from said vinyl monomer and saidfluoromonomer in said copolymeric backbone.
 2. The process as recited inclaim 1 wherein the co-solvent is unreactive or substantially unreactivewith the copolymer.
 3. The process as recited in claim 1 wherein theco-solvent is selected from the group consisting of acetic acid,t-butanol, acetonitrile, and methyl acetate.
 4. The process as recitedin claim 1 wherein said solvent is acetic acid.
 5. The process asrecited in claim 4 wherein the amount of co-solvent contained in saidaqueous reaction medium is from about 1 to about 50% by weight of saidmedium.
 6. The process as recited in claim 5 wherein said amount is fromabout 10 to about 45% by weight.
 7. The process as recited in claim 6wherein said amount is from about 15 to about 40% by weight.
 8. Theprocess as recited in claim 5 wherein the fluoromonomer istetrafluoroethylene.
 9. The process as recited in claim 1 wherein thevinyl monomer is vinyl acetate.
 10. The process as recited in claim 1wherein the amount of vinyl monomer is an amount capable of dissolvingin said reaction medium without forming a distinct vinyl monomer phase.11. The process as recited in claim 10 wherein maintaining said molarratio comprises adding additional vinyl monomer to said reaction mediumas vinyl monomer in said medium is consumed at a rate based on the rateof fluoromonomer consumption.
 12. The process as recited in claim 1wherein said co-polymerizing is carried out in an inert atmosphere. 13.The process as recited in claim 1 wherein copolymerizating said monomersand maintaining said molar ratio comprises:charging a reaction vesselwith said aqueous reaction medium, polymerization initiator and aselected amount of said vinyl monomer which does not exceed thesolubility thereof in said aqueous medium in an inert atmosphere;charging said vessel with a gaseous fluoromonomer until said pressurereaches a selected value which corresponds to a selected concentrationof fluoromonomer in said reactor; and copolymerizing said fluoromonomerand said vinyl monomer while adding fluoromonomer at a rate sufficientto maintain said pressure at said selected value and adding additionalvinyl monomer at a rate sufficient to maintain the concentration ofvinyl monomer dissolved in the aqueous reaction medium at the selectedamount.
 14. The process as recited in claim 12 wherein the rate ofaddition of said additional vinyl monomer is based on the rate ofconsumption of fluoromonomer in said reactor.
 15. The process as recitedin claim 1 wherein the initiator is an oxidation-reduction systemcomprising an oxidizing agent and a reducing agent.
 16. The process asrecited in claim 15 wherein the oxidizing agent is a water solublealkali metal or alkaline earth metal salt of persulfuric acid or anammonium salt of persulfuric acid.
 17. The process as recited in claim16 wherein the oxidizing agent is ammonium persulfate.
 18. The processas recited in claim 17 wherein the reducing agent is selected from thegroup consisting of ammonium or alkali metal sulfites, thiosulfites,thiosulfites, bisulfites, hydrosulfites, and ascobic acid.
 19. Theprocess of claim 1 wherein the degree of alternation of the fluorinatedunits and vinyl units in said copolymer is at least about 60%.
 20. Theprocess of claim 1 wherein the degree of alternation of the fluorinatedunits and vinyl units in said copolymer is from about 40% to about 60%.21. The process of claim 19 wherein said degree of alternation is fromabout 60% to about 80%.
 22. The process of claim 19 wherein saidcopolymer has an intrinsic viscosity at 35° C. in dimethyl formamideaccording to the procedure of ASTM D-1238 equal to or greater than about0.5.
 23. The process of claim 22 wherein said intrinsic viscosity isfrom about 0.5 to about 2.5.
 24. The process of claim 1 wherein saidcopolymer has an intrinsic viscosity at 35° C. in dimethylformamideaccording to the procedure of ASTM D-1238 of from about 0.2 to about2.5.
 25. The process of claim 24 wherein said intrinsic viscosity isfrom about 0.3 to about 1.3.
 26. The process of claim 25 wherein saidintrinsic viscosity is from about 0.5 to about 1.2.
 27. The process ofclaim 22 wherein said copolymer comprises from about 45 to about 55 molepercent of fluorinated units and correspondingly from about 55 to about45 mole percent of vinyl units.